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Selective Retransmission of MPEG Video Streams over IP Networks

Selective Retransmission of MPEG Video Streams over IP Networks. Árpád Huszák, Sándor Imre Budapest University of Technology and Economics Department of Telecommunications Mobile Communications and Computing Laboratory Phoenix project. Motivation.

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Selective Retransmission of MPEG Video Streams over IP Networks

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  1. Selective Retransmission of MPEG Video Streams over IP Networks Árpád Huszák, Sándor Imre Budapest University of Technology and Economics Department of Telecommunications Mobile Communications and Computing Laboratory Phoenix project

  2. Motivation • Multimedia streaming is becoming increasingly popular in IP networks • New wireless technologies • 3G, 4G mobile networks • WiMAX • WLAN • Two major issues arise in spite of the popularity of multimedia applications in mobile networks • limited bandwidth restricts high bit rate video transmission • wireless transmission by its nature may introduce higher rate of errors during transmission

  3. Introduction • Multimedia applications in mobile networks • Transmission over unreliable wireless channels • The frequent errors should cause deterioration of the quality of multimedia streams • Delay and packet loss caused by handovers • New method to increase the quality of audio/video streams in mobile environment • Differentiation of packets within a media stream • Selective retransmission of important packets

  4. Selective retransmission • Differentiation of packets within an MPEG media stream • MPEG frames • (I) Intra frame coded, key-frame (max. priority) • (P) Predicted • (B) Bidirectional • Error in a key-frame (I) propagates to all other frames till the next key-frame • It is advisable to handle these frames on a different way • Retransmission of the damaged part of the key-frame will significantly raise the quality of the video stream

  5. Selective retransmission • Transport protocol for selective retransmission • Unreliable (no automatic retransmission) • Packet numbers • Acknowledgements • Information on lost packets • Information about the network (RTT) • Congestion control (TCP-like, TFRC) • DCCP • RFC4340, March 2006 • think of DCCP as TCP minus bytestream semantics and reliability • or as UDP plus congestion control, handshakes, and acknowledgements DCCP Datagram Congestion Control Protocol

  6. Buffer 1 MPEG fragmentation (I,P,B) Packetizer -packet length -header (IP,DCCP) MPEG Channel (pbit) Buffer 2 Checksum calculation (retransmission request) MPEG Depaketizer Selective retransmission scheme • Packet identifying • Temporal storage of dedicated packets in buffers • Delete only when acknowledgement arrives • Each DCCP packet has an individual sequence number that makes possible to detect packet losses

  7. Examination • The packet drop probability • The retransmission probability is calculated as follows • In case of interactive media the RTT must be analyzed to decide whether the total delay is acceptable. In our solution the delay is

  8. Examination The retransmission probability in the function of size(I)/size(GoP) ratio according to the actual channel bit-error probability Retransmission probability in function of bit-error probability

  9. Examination • Comparison of UDP, UDPLite and DCCP Retransmission Algorithm • There are N frames in a GoP, therefore single I-frame bit correction leads to the improvement of N bits increasing the MPEG quality significantly

  10. Testbed • DCCP Selective Retransmission testbed • Linux 2.6.14 • Client-Server side applications • Adjustable packet loss ratio

  11. Results • Visible difference in MPEG video quality • Our algorithm radically reduces the bit corruption ratio and achieves significant increase of quality With Sel. Retr. Original Without Sel. Retr.

  12. Results • MPEG - peak-to-peak signal-to-noise ratio (PSNR) [dB] • 3-4 dB gain was achieved with our Selective Retransmission method

  13. Future plans • The additional delay caused by our method should be examined • Time and bandwidth limitations should be examined • The algorithm can be extended to allow multiple retransmissions realizing TCP-like reliable transmission • The evaluations were done on MPEG streams, but the selective retransmission algorithm is capable for other data type transmissions where the data can be differentiated

  14. Conclusion • In this presentation a new selective retransmission algorithm was presented and studied • The results obtained show that the algorithm • radically reduces the bit corruption ratio • achieves significant increase of quality especially in wireless networks with high bit-error ratio

  15. Thank you for yourattention!

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